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              <h1>看了好几遍 synchronized与ReentrantLock 的区别 - 交互式测验</h1>
              <p>检验你对文档内容的理解程度</p>
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  {
    "question": "根据文档，在使用 `ReentrantLock` 进行编程时，为什么强烈推荐将 `lock.unlock()` 调用放置在 `finally` 代码块中？",
    "options": [
      "这是一种过时的编码习惯，现代JVM会自动处理。",
      "为了确保即使在受保护的代码块中发生异常，锁也能被可靠地释放，从而避免死锁。",
      "因为 `finally` 块中的代码执行优先级最高，可以更快地释放锁，提升性能。",
      "主要是为了提高代码的可读性，功能上并无特殊作用。"
    ],
    "correctAnswerIndex": 1,
    "explanation": "文档中的“正确姿势”明确指出，`lock.unlock()` 必须放在 `finally` 块中。这是因为如果在 `try` 块的业务逻辑中发生异常，程序流程会中断，如果没有 `finally` 块，`unlock()` 方法将不会被执行。这会导致锁永远不会被释放，其他等待该锁的线程将无限期地阻塞，造成死锁。",
    "source": "文档中「八、常见误区与陷阱」部分的「误区2：忘记释放ReentrantLock」和「正确姿势」",
    "hint": "文档中提到了一个“危险”的示例，其中如果发生异常，某个关键的释放操作可能永远不会执行。"
  },
  {
    "question": "关于 `synchronized` 和 `ReentrantLock` 在“公平性”方面的差异，以下哪个描述是完全正确的？",
    "options": [
      "`synchronized` 默认是公平锁，可以通过JVM参数配置为非公平锁。",
      "`ReentrantLock` 可以在创建时选择成为公平锁或非公平锁，而 `synchronized` 始终是非公平锁。",
      "两者都支持公平和非公平两种模式，但 `ReentrantLock` 的性能更好。",
      "`ReentrantLock` 始终是公平锁，遵循先到先得的原则，而 `synchronized` 是非公平的。"
    ],
    "correctAnswerIndex": 1,
    "explanation": "对比表格明确指出，`synchronized` 的公平性是“非公平”，而 `ReentrantLock` 则是“可选公平/非公平”。这意味着开发者可以在创建 `ReentrantLock` 实例时（通过构造函数 `new ReentrantLock(true)`)来决定是否启用公平策略。公平锁保证了线程获取锁的顺序与它们发出请求的顺序一致，而非公平锁则允许“插队”，可能会有更高的吞吐量。",
    "source": "文档中「五、全方位对比：九大维度深度解析」表格中的「公平性」一行",
    "hint": "查阅文档中的对比表格，关注“公平性”维度是如何描述这两种锁的。"
  },
  {
    "question": "假设一个业务场景需要线程在尝试获取锁时，如果等待超过特定时间仍未成功，就放弃并执行备用逻辑。根据文档，哪种锁机制及其特性最适合实现此需求？",
    "options": [
      "`synchronized`，因为它内置了可中断的特性。",
      "`ReentrantLock`，因为它提供了 `tryLock()` 方法，支持带超时的获取锁操作。",
      "两者都可以，通过 `Thread.sleep()` 和循环判断来实现。",
      "`synchronized` 结合 `wait(timeout)` 方法可以实现相同的效果。"
    ],
    "correctAnswerIndex": 1,
    "explanation": "文档中明确演示了 `ReentrantLock` 的高级功能，其中 `lock.tryLock(5, TimeUnit.SECONDS)` 方法允许一个线程在指定的时间内尝试获取锁。如果在超时时间内未能获取，它会返回 `false` 而不是继续阻塞，这使得实现超时放弃的逻辑变得非常直接和优雅。`synchronized` 关键字本身不提供这种可定时的、非阻塞的获取锁的能力。",
    "source": "文档中「四、ReentrantLock解决方案：功能强大的'手动挡'」部分的「高级功能演示」",
    "hint": "文档中有一个代码示例演示了如何在“5秒超时”内尝试获取锁。"
  },
  {
    "question": "从实现层面上看，`synchronized` 和 `ReentrantLock` 最根本的区别是什么？",
    "options": [
      "`synchronized` 是JDK提供的API，而 `ReentrantLock` 是JVM内置的关键字。",
      "两者都是基于AQS（AbstractQueuedSynchronizer）框架实现的。",
      "`synchronized` 是JVM内置的关键字，其实现与JVM紧密相关；而 `ReentrantLock` 是一个纯Java实现的类库（API），基于AQS框架。",
      "`synchronized` 的性能总是低于 `ReentrantLock`。"
    ],
    "correctAnswerIndex": 2,
    "explanation": "文档的核心对比部分和底层原理探秘部分都强调了这一点：`synchronized` 是Java语言的关键字，由JVM直接支持和实现，涉及到对象头中的标记位和操作系统的互斥量。而 `ReentrantLock` 是JDK `java.util.concurrent.locks` 包下的一个类，它是通过Java代码实现的，其核心同步机制依赖于AQS框架。",
    "source": "文档中「五、全方位对比：九大维度深度解析」表格的「锁类型」一行，及「九、锁的底层原理探秘」部分",
    "hint": "回顾对比表格中的第一行“锁类型”，它描述了两者在来源上的本质差异。"
  },
  {
    "question": "文档提到了`synchronized`的锁升级过程，这是JVM的一种优化手段。当一个对象锁在高并发下被激烈争用时，它最终会处于哪种状态？",
    "options": [
      "偏向锁 (Biased Lock)",
      "轻量级锁 (Lightweight Lock)",
      "重量级锁 (Heavyweight Lock)",
      "无锁状态 (Lock-Free)"
    ],
    "correctAnswerIndex": 2,
    "explanation": "根据文档中描述的 `synchronized` 锁升级路径，当线程竞争加剧，自旋等待（轻量级锁）也无法很快获得锁时，锁会膨胀为重量级锁。在这种状态下，获取不到锁的线程会被挂起，交由操作系统内核进行调度，这涉及到用户态和内核态的切换，因此开销较大，被称为“重量级”。",
    "source": "文档中「九、锁的底层原理探秘」部分的「synchronized的锁升级过程」",
    "hint": "文档中描述了锁状态从简单到复杂的演进过程，想想竞争最激烈时对应的是哪个阶段。"
  },
  {
    "question": "根据文档的“最佳实践”部分，在何种场景下应优先推荐使用 `synchronized`？",
    "options": [
      "当需要公平锁机制来避免线程饥饿时。",
      "当需要使用多个条件变量（Condition）来精确控制线程等待和唤醒时。",
      "当同步需求相对简单，且希望代码侵入性小、复杂度低时。",
      "当需要查询锁的当前状态，例如某个锁是否被持有。"
    ],
    "correctAnswerIndex": 2,
    "explanation": "文档的“最佳实践”指南中明确指出，`synchronized` 适用于“简单的代码块同步”、“对象级别锁足够时”和“需要最低限度的代码侵入”。它的语法简洁，且由JVM自动管理锁的获取与释放，降低了出错的风险，非常适合那些不需要 `ReentrantLock` 所提供的高级功能的常规同步场景。",
    "source": "文档中「七、最佳实践：选择锁的六大场景指南」部分的「推荐synchronized」",
    "hint": "想一想哪种锁被比喻为“简单可靠的'自动锁'”，适用于什么样的场景。"
  },
  {
    "question": "文档中的性能测试结果表明，在高并发下 `ReentrantLock` 的吞吐量和平均响应时间优于 `synchronized`，但这通常伴随着什么代价？",
    "options": [
      "代码复杂度显著降低。",
      "更高的CPU占用率和略高的内存消耗。",
      "与旧版本JDK的兼容性更差。",
      "无法实现可重入特性。"
    ],
    "correctAnswerIndex": 1,
    "explanation": "测试结果表格显示，`ReentrantLock` 在吞吐量（2841 vs 2356 ops/ms）和平均响应时间（3.5 vs 4.2 ms）上表现更优。但同时，它的CPU占用率（85% vs 78%）和内存消耗（534 vs 512 MB）也略高于 `synchronized`。这说明其高性能是通过消耗更多计算和内存资源换来的。",
    "source": "文档中「六、实战性能测试：10万并发抢购对比」部分的「测试结果」表格和结论",
    "hint": "仔细查看性能测试表格中，`ReentrantLock` 除了性能指标占优外，还有哪些指标数值更高？"
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            }
        }

        function showFinalScore() {
            document.querySelector('.quiz-body').style.display = 'none';
            document.getElementById('quiz-footer').style.display = 'none';

            const correctCount = score;
            const totalQuestions = quizData.length;
            const answeredCount = userAnswers.filter(a => a !== null).length;
            const wrongCount = answeredCount - correctCount;
            const skippedCount = totalQuestions - answeredCount;
            const accuracy = totalQuestions > 0 ? Math.round((correctCount / totalQuestions) * 100) : 0;
            const errorRate = totalQuestions > 0 ? Math.round((wrongCount / totalQuestions) * 100) : 0;

            const finalScoreHtml =
                '<div class="final-score-container">' +
                '<h2>答题报告</h2>' +
                '<div class="score-summary">' +
                '<div class="score-card">' +
                '<h3>得分</h3>' +
                '<p>' + correctCount + ' / ' + totalQuestions + '</p>' +
                '</div>' +
                '<div class="score-card">' +
                '<h3>正确率</h3>' +
                '<p>' + accuracy + '%</p>' +
                '</div>' +
                '<div class="score-card">' +
                '<h3>错误率</h3>' +
                '<p>' + errorRate + '%</p>' +
                '</div>' +
                '<div class="score-card score-details">' +
                '<table>' +
                '<tr><td>正确</td><td>' + correctCount + '</td></tr>' +
                '<tr><td>错误</td><td>' + wrongCount + '</td></tr>' +
                '<tr><td>未答</td><td>' + skippedCount + '</td></tr>' +
                '</table>' +
                '</div>' +
                '</div>' +
                '<div class="report-actions">' +
                '<button id="review-btn">回顾测验</button>' +
                '<button class="primary" onclick="location.reload()">再试一次</button>' +
                '</div>' +
                '</div>';

            let reportEl = document.querySelector('.final-score-container');
            if (reportEl) {
                reportEl.remove();
            }
            quizContentEl.insertAdjacentHTML('beforeend', finalScoreHtml);
            document.getElementById('review-btn').addEventListener('click', reviewQuiz);
        }

        function reviewQuiz() {
            const reportEl = document.querySelector('.final-score-container');
            if (reportEl) {
                reportEl.remove();
            }

            document.querySelector('.quiz-body').style.display = 'block';
            document.getElementById('quiz-footer').style.display = 'flex';
            
            currentQuestionIndex = 0;
            loadQuestion();
            updateNavigationButtons(); // Ensure nav buttons are correctly displayed
        }

        // Event Delegation for options
        optionsListEl.addEventListener('click', (event) => {
            if (event.target && event.target.matches('li.option-item')) {
                // Check if the question has already been answered
                if (userAnswers[currentQuestionIndex] === null) {
                    const selectedIndex = parseInt(event.target.dataset.index, 10);
                    selectOption(selectedIndex);
                }
            }
        });

        prevBtn.addEventListener('click', goToPreviousQuestion);
        nextBtn.addEventListener('click', goToNextQuestion);
        hintBtn.addEventListener('click', showHint);
        
        // 初始加载
        loadQuestion();
      </script>
    </body>
    </html>
  